The apparatus using an upper and lower ball screw rod, of which thread cut directions are opposite with each other and an upper and lower nut member threadedly engaging respectively therewith and mounted respectively with an upper and down table respectively carrying an upper and down tool part has been actually used and in public knowledge.
However, in such apparatus the upper and lower tool parts are symmetrically moved toward or apart with each other always at a same rate. Those skilled in the art may understand that it is necessary or preferable to drive the two tool parts asymmetrically so to speak in such engineering work. For instance, one part only is moved while the other is stopped, one part is slowly moved but the other is rapidly moved, or the two parts are time-differentially moved.